Update on Safety and Efficacy of HPV Vaccines: Focus on Gardasil

The human papillomavirus (HPV) is a highly contagious and prevalent virus that is primarily sexually transmitted. The Gardasil® quadrivalent vaccine, the Cevarix® bivalent vaccine and the Gardasil® 9 nonavalent vaccine were developed to prevent the spread of HPV as well as the incidence of its associated diseases. The aim of this mini-review is to critically analyze the safety and efficacy of both the Gardasil vaccines. A literature search was conducted on ProQuest, MedLine, Science Direct and Scopus databases. More than hundred articles were scanned, and from this, 38 most relevant papers involving human studies across several countries were closely reviewed. The literature deems the Gardasil® HPV vaccines to be safe and efficacious. Due to the novel nature of these vaccines, long-term efficacies, as well as their associated long-term adverse effects, are yet to be confirmed. Of some concern was the finding that a majority of these studies disclosed minor to major involvement with the vaccine manufacturers, and the inhibitory cost of use in developing nations. Gardasil is largely considered safe to use. However, considering that these vaccines are predominantly indicated for children, further comprehensive, impartial, and long-term studies are needed to critically assess safety and efficacy.

This allows for the body's development of endogenous antibodies against the genotypes (Table   1), providing a mechanism to develop long-term immunity against the virus. However, these vaccines do not have the capability to treat any preexisting HPV infections or related conditions. Vaccine efficacy is difficult to determine due to the lengthy bout of time from viral exposure to disease onset, thus eluding to the possibility of undetectable flaws in the effectiveness and safety of these vaccines.
The development of these vaccines (Figure 1) allowed for a multi-faceted approach to their mechanism of immunity. Foremost, as previously mentioned, the neutralising antibodies play the focal role in defence against the various virus genotypes (Table 1), rather than cell-mediated immunity. The vaccines readily generate these neutralising antibodies, which continue to deactivate the virus in elevated and enduring titres.
This phenomenon is typically limited to genotypes found in the vaccine and is minimally observed in cross-type protection of other genotypes, although studies vary in degree and duration of crossprotection, as will be discussed later. Moreover, these vaccines allow for negligible risk of viral transmission and produce significant antibodymediated suppression due to the virus' innate vulnerability.
The aim of this review is to critically analyze the safety and efficacy of the Gardasil® vaccine, both the quadrivalent and nonavalent varieties.
Safety would be characterized as the adverse effects associated with the vaccinations whereas efficacy would be illustrated via various defined end-points.
We performed a multi-study review of current  solution. They observed injection associated muscle fibre degeneration, described as swelling of myofiber tissue, sarcoplasm fragmentation resulting in inflammation, and consequently, the presence of inflammatory mediators. Admittedly, caution must be taken when extrapolating animal data to humans, and further testing is required.  (17). Among the 152 reported adverse events, the majority were local injection site reactions (20%), rash (22%), non-anaphylactic allergic reactions (25%), and other severe or unusual events (26%) (15). They concluded that the incidence of AEFI were quite low and concurrent with those reported elsewhere (17,23).

Safety in females
An observer-blinded study was conducted to determine the safety profile of a two or three dose schedule of the quadrivalent vaccine compared to two doses of the bivalent vaccine (2). 4% of the participants reported at least one serious adverse effect, half of which were from the group receiving two doses of the bivalent vaccine while the remainder were from the groups receiving two or three doses of the quadrivalent vaccine. However, the investigators of this study determined that none of these serious adverse effects were vaccine related.

Safety in males
A study was conducted on heterosexual and homosexual men to ascertain the safety of the quadrivalent vaccine compared to women (15).
Males in this mixed gender study reported fewer adverse effects than women in the same study. This may be due to the reluctance of men to report such effects as a result of societal masculine pressures or norms. The reported AEFI were mostly injection site reactions of mild to moderate pain intensity.

Safety in immunocompromised persons
Immunocompromised persons are especially prone to infections that are viral or bacterial in nature. Diseases such as HPV are much more prevalent in immunocompromised populations due to their weakened or impaired immune systems (7,11,13,24,25).
The use of vaccines to prevent HPV related diseases in this population has been disputed and research has been conducted to perform risk-benefit analyzes. In a study composed of 34 female participants with systemic lupus erythematosus (SLE), the reported adverse effects were comparable to healthy women receiving the vaccine. There was no associated increase in hospitalisations or emergency situations postimmunisation, and vaccination was considered as generally safe (7).
Unlike with influenza vaccines, the administration of the 4vHPV has not caused any transient demyelinating disorder. Thus, the vaccine was well tolerated and they did not encounter SLE symptomatic flare ups or production of autoantibodies.
In a study conducted on HIV infected persons, the effect of the quadrivalent vaccine was observed and compared to non-HIV infected persons (13).
The quadrivalent vaccine was generally well tolerated, many participants reported local pain at injection site: 18.8% of HIV negative and 32.6% of HIV positive participants (11,13).
These results were concurrent with previous data, specifically similar for HIV positive participants. Nonetheless, results in this study were lower in HIV negative participants than in other studies (13). This indicates inconsistencies, and suggests that further research is required.

Efficacy
Research on the efficacy of the Gardasil® vaccine has been widespread as shown in Table 3.
To determine efficacy, the use of cancer diagnoses as endpoints is unethical and unachievable due to the long lag time from infection to cancer, which may take 7-10 years or more. Thus, each study Another study involving male participants found that the GMTs for heterosexual men (HM) were non-inferior to their female counterparts.9vHPV vaccination seems less efficacious (weaker antibody response) in men who have sex with men (MSM) than HM. This was illustrated in a higher GMTs among all nine HPV types in HM than MSM. (5) 4vHPV Cytology results were obtained at cervical screening and three year absolute and RR with 95% of ≥ CIN2; results were compared in those who had been vaccinated and unvaccinated (reference group) Correspondingly, the entire vaccination process has changed the clinical interpretation of cervical screening results. Three-year risk analyzes were performed and determined to be 5.26% and 0.99% for ≥ CIN2 and ≥ CIN3, respectively, in women that were vaccinated before 18 years of age (95% CI). Conversely, unvaccinated women were found to have a risk of 10.89% and 3.7% for ≥ CIN2 and ≥ CIN3, respectively. The authors of this study, consequently, recommend cervical examinations to be performed at a younger age. (9) 4vHPV VE was based on the prevalence of HPV in the vaccinated and unvaccinated pregnant women; it was calculated as VE = 1 -OR An exploratory study into a cohort of pregnant women was performed in Montreal from 2010-2016 to determine the effectiveness of the quadrivalent vaccine. They concluded that the incidence of HPV16/18 was significantly higher among unvaccinated pregnant women (7.2%) compared to vaccinated pregnant women (1.3%). They also reported a statistically significant vaccine effectiveness score (86.1%), adjusted for age and number of sexual partners in the past year, in those that were vaccinated. (10) 2vHPV 4vHPV Genital swabs and serum were tested for the presence of anti-HPV16/18/31/45 antibodies and analyzed by VLP ELISA to obtain GMT which was normalised to the total IgG present in the sample; titres were deemed neutralising at ≥ 20 Draper et al. concluded that among the GMT anti-HPV16 (146,979 and 45,220; P<0.001) and 18 (81,434 and 17,907; P<0.001) antibody titres detected, Cevarix® was more efficacious than Gardasil®, respectively. Similarly, the levels for Cevarix® seemed to be higher than that of Gardasil® in regards to the non-vaccine types HPV31/45 as well, with 356 and 124 (P<0.001) and 35 and 13 (P<0.001), respectively. (11) 2vHPV 4vHPV Anal and cervical swabs were obtained and anti-HPV antibodies were measured using a multiplex In one study, the participants were divided into two groups, each being administered with the bivalent or quadrivalent vaccines. Among the pseudovirion binding assay to determine HPV type-specific IgG antibodies male and female HIV positive participants, the bivalent appeared to cause 100% seroconversion for both HPV16/18. Whereas, the quadrivalent showed seroconversion for HPV16 in men (100%) and women (90%) and HPV18 in men (63%) and women (91%) at much lower rates. (14) 2vHPV 9vHPV Serum samples were tested for the presence of anti-HPV6/11/16/18/31//33/45/52/58 and measured using multiplex direct IgG ELISA; seropositivity was determined if anti-HPV serum levels were 0.1 AU/mL, 0.1 AU/mL, 0.5 IU/mL, 0.4 IU/mL, 1.3 AU/mL, 2.5 AU/mL, 0.7 AU/mL and 1.2 AU/mL, respectively In a mixed-gender mixed-vaccine scheduled study, girls and boys were subjected to either two doses of 9vHPV vaccine or a mixed dose of 9vHPV and 2vHPv. They found that anti-HPV16/18 GMTs were higher in those that received the 2vHPV vaccine than those who received two doses of the 9vHPV vaccine; though, the remaining HPV subtype GMTs (6/11/31/45/5/58) were all higher among those who received two doses of the 9vHPV vaccine. (15) 4vHPV Anti-HPV antibodies were measured using cLIA; antibody levels were reported as mMU/mL In a study conducted on men, participants from Mexico exhibited lower anti-HPV18 antibody responses than those residing in the USA, with 286.5 and 314.8 respectively. However, the anti-HPV16 antibody titres were the same, 45 times higher at 7 months post immunisation than on day 1. They also found that vaccine efficacy was equivalent among mid-aged men (27-45 years) and younger men, for whom the vaccine is clinically indicated. (16) 2vHPV 4vHPV Serum was tested for the presence of anti-HPV16/18/31/45 antibodies and analyzed by VLP ELISA to obtain GMT The authors continued their research and published corroborated results six years later (8).
Neutralising antibodies were detected more than 7 years after the initial vaccine administration. They found that the Cevarix® titres continued to be higher than its counterpart, Gardasil®. This may suggest that the bivalent vaccine may be more effective than the quadrivalent vaccine yet, more research is required. (18) 2vHPV 4vHPV Cervical sample obtained and was analyzed via an HPV PCR-ELISA method using HRHPV and LRHPV probes; results were then genotyped to determine prevalence and compared to HPV vaccine clinical trial data In a large scale, randomised, double-blind trial, the incidence of high grade cervical, vulvar and vaginal disease associated with HPV31/33/45/52/58 was found to be 0.5 cases per 10,000 persons among those that received the 9vHPV vaccine compared to 19 cases per 10,000 persons in those that received the 4vHPV vaccine. According to these findings, the researchers calculated a 97.4% VE rating with a 95% CI. Furthermore, they found non-inferior HPV6/11/16/18 GMTs in the 4vHPV versus 9vHPV up to 3 years post-vaccination. They concluded that the 9vHPV could provide more comprehensive coverage and should be implemented worldwide. (21) 4vHPV Cervical samples were obtained and analyzed for incidence of ICC and CIN3+; VE = 1incidence rate among vaccinated / incidence rate among unvaccinated participants  In short, studies suggest that the Gardasil® HPV vaccines are generally well tolerated and produce adequate immunity. Even so, the authors of this paper wish to express the importance of further comprehensive, scrupulous and impartial analyzes on these internationally utilised vaccines.
Therefore, future research needs to be conducted to ratify the risk-benefit analyzes of these vaccines.